Articles prepared from resin compositions which have improved resistance to elevated temperatures are desirable for many applications. In particular these articles, having improved elevated temperature resistance, are desirable for printed circuit board applications due to industry trends which include higher circuit densities, increased board thickness, lead free solders, and higher temperature use environments.
Articles such as laminates, and particularly structural and electrical copper clad laminates, are generally manufactured by pressing, under elevated temperatures and pressures, various layers of partially cured prepregs and optionally copper sheeting. Prepregs are generally manufactured by impregnating a thermosettable epoxy resin composition into a porous substrate, such as a glass fiber mat, followed by processing at elevated temperatures to promote a partial cure of the epoxy resin in the mat to a “B-stage.” Complete cure of the epoxy resin impregnated in the glass fiber mat typically occurs during the lamination step when the prepreg layers are pressed under high pressure and elevated temperatures for a time sufficient to allow for complete cure of the resin.
Epoxy resin compositions which impart enhanced thermal properties are desirable in the manufacture of prepregs and laminates. Such systems offer improved heat resistance and reduced thermal expansion required for complex printed circuit board circuitry and for higher fabrication and usage temperatures. However, such resin compositions are typically more expensive to formulate and may suffer from inferior performance capabilities.
U.S. Pat. Nos. 6,451,878 and 5,081,206, for example, disclose the use of several advancement or upstaging catalysts, including alkali metal hydroxides, for the reaction between an epoxy group and a phenolic hydroxyl group for the preparation of higher molecular weight epoxides.
U.S. Pat. No. 5,380,804 discloses curable compositions which employ 1,3,5-tris-(2-carboxyethyl)isocyanurate crosslinker and an optional cure catalyst which may include phosphines, phosphates, amines, oxides, alkoxides, such as methoxide or ethoxide, hydroxides, such as sodium hydroxide or potassium hydroxide, carbonates, carboxylic salts, quaternary salts and the like.
U.S. Pat. No. 4,251,594 discloses an improvement for the preparation of electrical laminates in utilizing an alkali metal hydroxide as a catalyst for epoxy-phenolic hydroxyl fusion reaction.
U.S. Pat. No. 2,589,245 discloses complex amide-epoxide compositions and that alkaline and Friedel-Crafts type catalysts, including sodium hydroxide, potassium hydroxide and sodium phenoxide, are active in promoting the reaction of epoxide groups with amines.
However, the prior art does not teach or suggest the use of alkali metal containing compounds as an accelerator which may be used with curing agents for the cure of epoxy compounds to produce laminates, for printed circuit boards and non-electrical structural applications, having enhanced thermal properties.
In light of the above, there is a need in the art for epoxy resin compositions for preparing articles having improved thermal properties and for processes to produce them. There is also a need in the art for inexpensive resin compositions for achieving enhanced thermal properties and for articles, especially prepregs, having enhanced thermal properties.